In recent years, capacitance touch panels have been increasingly used in various mobile devices such as cellular phones and portable music players. Such capacitance touch panels have a structure in which a dielectric layer is laminated on a patterned conductor, and touching with a finger or the like establishes a ground via capacitance of a human body. In that case, there occurs a change in the value of resistance between a patterned electrode and a grounding point, and position input is recognized. However, when conventional transparent conductive films are used, there has been a problem in that a pattern is emphasized because of a great difference in optical properties between a part having a conductive layer and a part where the conductive layer is removed, which reduces visibility when disposed at a front of a display such as a liquid crystal display.
To not emphasize the transmittance and color tone of a transparent conductive film and, furthermore, the pattern of a conductive layer, methods have been proposed which are used for antireflection films and the like and utilize interference of light with layers having different refractive indices laminated. In other words, methods have been proposed which utilize optical interference with a layer having a different refractive index (also referred to as an index-matching layer, a refractive index-adjusting layer, an optically functional layer, an optically adjusting layer, or an antireflection layer) provided between a transparent conductive thin-film layer and a substrate film, and JP 2010-15861 A discloses “a transparent conductive laminated film having a structure in which a high refractive index layer, a low refractive index layer, and a transparent conductive thin-film layer are laminated in this order on a substrate made of a transparent plastic film, wherein the high refractive index layer has a refractive index in the range of 1.70 to 2.50 and a thickness in the range 4 to 20 nm, and the low refractive index layer has a refractive index in the range of 1.30 to 1.60 and a thickness in the range 20 to 50 nm.”
As an example of formation of the refractive index-adjusting layer described above by wet coating, Japanese Patent No. 3626624 discloses “a transparent conductive laminated body comprising an organic polymer substrate and a transparent conductive layer laminated on at least one outermost surface of the substrate, wherein (A1) a layer having a refractive index in the range from 1.7 to the refractive index of the transparent conductive layer+0.3 and a thickness in the range of 20 to 90 nm (H1 layer), (B1) a layer having a refractive index in the range of 1.35 to 1.5 and a thickness in the range of 30 to 110 nm (L1 layer), and (C) a transparent conductive layer having a thickness in the range of 12 to 30 nm are laminated on the substrate in this order; (D) the sum of optical thicknesses of the three layers is in the range of 180 to 230 nm; (F) the average reflectance of the lamination surface of the transparent conductive layer at a wavelength of 450 to 650 nm is 5.5% or less; and (G) the b* value of transmitted light of the laminated body, based on the psychometric chroma coordinates of the L*a*b* color system defined in Japanese Industrial Standard Z8729, is in the range of 0 to 2” and “the transparent conductive laminated body, wherein the H1 layer and/or the L1 layer are layers obtained mainly by hydrolysis and condensation of metal alkoxides.”
Further, as an example in which the outermost surface shape of a lower layer (underlying layer) of a transparent electrode layer is focused, JP 2011-183567 A discloses “a substrate with a transparent electrode, wherein an underlying layer composed mainly of partially or completely particulate silicon oxide, and a transparent electrode layer comprising a transparent conductive oxide layer composed mainly of indium oxide or zinc oxide are formed on the substrate in this order, and the underlying layer has an arithmetic average roughness (Ra) of 4 nm to 10 nm and a refractive index in the range of 1.34 to 1.60.”
The process of forming a conductive layer pattern from a transparent conductive film is generally performed by removing unwanted parts of a conductive layer by etching. In the etching process, alkaline solution is often used, and therefore a refractive index-adjusting layer of the transparent conductive film requires alkali resistance. One method of providing a laminated body with alkali resistance like this refractive index-adjusting layer is an antireflection layer with high alkali resistance, and as an example thereof, JP 2009-51045 A discloses “an antireflection film having a substrate film made of biaxially-stretched polyethylene terephthalate, a hard coat layer on the substrate film, and, furthermore, a low refractive index layer on the hard coat layer, wherein the hard coat layer has a thickness of 0.5 to 5 μm, and the hard coat layer is formed by blending 100 parts by mass of an ionizing radiation-curable resin comprising 80 to 97% by mass of polyfunctional (meth)acrylate having two or more (meth)acryloyl groups in its molecule and 20 to 3% by mass of N-vinylcaprolactam with 200 to 600 parts by mass of antimony pentoxide, and curing the blending.”
There are the following problems in the prior art mentioned above.
In JP '861 and JP '624, a high refractive index layer, a low refractive index layer, and a conductive layer are laminated on a substrate. However, according to the description of JP '861, the low refractive index layer is laminated by sputtering, and in JP '624, alkoxysilane hydrolysate is used. The refractive index described in Examples is about 1.46, but we determined that such a refractive index is insufficient to produce the effect of reducing coloring of transmitted light and the effect of making a pattern of a conductive layer less visible, and simply lowering the refractive index at the same constitution may compromise in-plane uniformity of the effect of making a pattern of a conductive layer less visible.
In JP '045, a high refractive index layer and a low refractive index layer are laminated on a substrate, but we determined that the alkali resistance is insufficient. Moreover, according to the method of evaluating alkali resistance described in Examples, when a conductive layer is formed on the high refractive index layer and the low refractive index layer, the alkali resistance is insufficient for the process of patterning the conductive layer.
In JP '567, a conductive layer is formed on an underlying layer composed mainly of particulate silicon oxide, but we determined that the effect of making a pattern of a conductive layer less visible and the effect of preventing coloring of transmitted light are insufficient.
In addition, in any of JP '861, JP '624 and JP '567, annealing is performed to improve the conductivity after forming a conductive layer, but the annealing temperature is as high as 170° C. or higher, which may cause deformation of a support substrate, heat shrinkage, precipitation of oligomer components, and the like.
It could therefore be helpful to provide a laminated body having a laminated film comprising a first layer and a second layer having different refractive indices on at least one surface of a support substrate, the laminated body having desired properties even if annealing for improving conductivity and light transmittance is carried out at a lower temperature when a conductive layer is laminated on the outermost surface of the laminated film to form a conductive laminated body, a method of producing the laminated body, and a coating composition for producing the laminated body.
It could also be helpful to provide a laminated body with high alkali resistance which is not affected when a conductive layer is formed on the outermost surface of the laminated film, or even if alkaline solution is used for patterning when the conductive layer is further patterned by etching, the laminated body further being able to reduce observation angle dependence and in-plane uniformity of the effect of reducing coloring of transmitted light and the effect of making a pattern of a conductive layer less visible, a method of producing the laminated body, and a coating composition for producing the laminated body.